Thunder

Thunder is an element that moves steadily down in a sort of zig-zaggy fashion. Although thought to move randomly, the steady flow of thunder from metal piece to metal piece in a 'Thunder Course' proves that it has a special course that depends on where it is started.

Reactions:
Thunder + Water = Water explodes like a firework.

Thunder + Metal = Thunder flows through the metal.

Thunder + Explosive/Flammable Material = The material reacts as it would to fire.